Opaque polymeric films in which the opacifying agent is finely divided polymer dispersed in the continuous film polymer phase are described in U.S. Pat. No. 4,377,616, which is incorporated herein by reference in its entirety. In the patent the film is prepared by melting a mixture of a major proportion of a film forming polymer such as polypropylene and a minor proportion of an incompatible polymer which has a higher melting point, such as nylon (polybutyleneterephthalate is also known to be useful), at a temperature sufficient to melt the incompatible polymer and to disperse it in the film forming polymer, extruding the mixture into a film and biaxially orienting the film. The dispersed incompatible polymer provides sites for the formation of voids surrounding the dispersed polymer particles when the film is oriented. These voids provide opacity and give the film an attractive pearlescent sheen.
U.S. Pat. No. 4,579,912 discloses blends of linear, low density copolymers and up to 10% aromatic polymers, e.g., polyparamethylstyrene, as a means of providing blown films having greater MD strength and higher stiffness compared to film containing the low density copolymers alone.
The instant invention is concerned with films having a high degree of or improved opacity.